If it is the GRAPH of a function from A to B that is a subset of A x B, then why do websites say that a function f is a subset of A x B? Such as this website on page 7 of 22 http://www.mathdb.org/notes_download/elementary/algebra/ae_A1.pd

Question

watchmath · Answer

well a function is a special relation. If a is related to b by a relation we write it as aRb. But to   make it more convinient we just write it as (a,b) to say that aRb.

anonymous · Answer

So you are saying that a function is already a set of ordered pairs/?

watchmath · Answer

strictly speaking functions is the rule that relates an ordered pairs. But if we are given the ordered pairs then we know how the rule behave.